How is the current in heart flowing?
From area of depolarization to polarized areas
Electrical potentil generated can be represented by what?
A vector, with arrowhead pointing in positive direction
Length of vector is proportional to what?
To voltage of potential
Generated potential at any instance can be represented by what?
An instantaneous mean vector
What does QRS complex represent?
Ventricular depolarization beginning at ventricular eptum and proceeds toward apex of heart with an average direction of 59 degrees
What does ventricular T wave represent?
It represents repolarization of ventricle that begins near apex of heart and proceeds toward the base
What does the atrial P wave represent?
Depolarization of the atria that begins at sinus node and sprads in all directions
What is shifting the mean electrical axis of ventricles to left?1
During expiration or when a person is recumbent and abdominal contents press upward against the diaphragm
What is shifting the mean electrical axis of ventricles to left?2
Accumulation of abdominal fat, which presses upward on the heart
What is shifting the mean electrical axis of ventricles to left?3
Left bundle branch block, which is when the cardiac impulse spreads through the right ventricle two to three times as fast in the left ventricle, consequently, the left ventricle remains polarized much longer than right, and strong electrical vector points from right ventricle to left
What is shifting the mean electrical axis of ventricles to left?4
Hypertrophy of left ventricle, caused by hypertension, aortic valvular stenosis, or aortic valvular regurgitation
WHich are the factors that shift the mean electrical axis of ventricles to the right (Clockwise)?
Inspiration, standing up, lack of abdominal fat which allows heart to rotate clockwise compared with normal individual, right bundle branch block, right ventricular hypertrophy
What does hypertrophy of heart do?
It increases the voltage of QRS complex
What is the most common cause of highvoltage QRS complexes?
Right or left ventricular hypertrophy
Which are the conditions causing decrease in voltage of QRS complex?1
Hearts with old myocardial infarctions and the resultant decreased cardiac muscle mass
Which are the conditions causing decrease in voltage of QRS complex?2
Conditions surrounding heart that effectively ''short-circuit'' the cardiac electrical potential. FLuid in pericardium and pleural effusion both conduct currents form around the heart and prevent much of votlage from reaching the surface of body (Pulmonary emphysema also decreases conduction of cardiac potentials)
What is the most common cause of an extended QRS complex?
Prolonged conduction through ventricles (occuring in both hypertrophied and dilated hearts and increasaes the duration of QRS waves)
What is the most common cause of an extended QRS complex?2
Blockade of impulses in Purkinje system prolongs the QRS complex because the duration of ventricular depolarization increases in one or both ventricles
What is current of injury?
Several abnormalities cause a portion of heart to remain depolarized all of the time, and the current that flows from depolarized area to polarize areas of heart is called current of injury
Which are some of the abnormaliteis that can cause a current of injury?
Mechanical trauma, infectious processes that damage the cardiac muscle membrane, coronary ischemia
What can the axis of current of injury be determined with?
How is the axis of current of injury determined?
1. Determine J point (point of zero potential at end of QRS wave) 2. Determine level of T-P segment with respect to J point on three standard leads 3. Plot the voltages on the coordinates of three leads to determine the axis of current of injury, and note that the negative end of vector originates in the injured area of ventricles
What is the current of injury useful for determining?
Whether an infarction is in anterior or posterior portion of heart
Which are the conditions that alter (change the electrical axis of T wave)?1
During bundle branch block, one of ventricles depolarizes before the other. The first ventricle to depolarize is also the first to repolarize, and this causes an axis deviation in the T wave. Therefore, a left bundle branch block causes a rightwar daxis deviation of T wave
What are the most common cause of shortened depolarization?
Mild ischemia of cardiac muscle in the base of ventricles
What does ventricular T wave represent?
Repolarization of ventricle
What does atrial P wave represent?
Depolarization of atria (beginning at sinus node and spreads in all directions)
What does left bundle branch block mean?
When cardiac impulse spreads through right ventricle faster than left ventricle, so left ventricle remains polarized much longer than right, and a strong electrical vector points from right ventricle to the left
What is hypertrophy of left ventricle caused by?
By hypertension, aortic valvular stenosis, or aortic valvualr regurgitation
How is Lead I recoreded?
From two electrodes placed respectively on the two arms (0 degrees)
What does vector A represent?
The instantaneous mean direction of curent flow in ventricles (can be 55 degrees)